A radiation delivery waveguide of the kind to which the present invention refers is, inter alia, described in PCT/US95/04915, the entire disclosure of which is incorporated herein by reference.
The radiation delivery waveguide described in PCT/US95/04915 is used in a guided radiation receiver assembly comprising a first transparent medium with a first refraction index n.sub.1 and a receiver chamber having an aperture and holding a second transparent medium having a second refraction index n.sub.2. The waveguide is transparent and has a third refraction index n.sub.3 substantially equal to or greater than n.sub.1. The transparent radiation delivery waveguide has a first, radiation intake portion in optical contact with the first transparent medium and held tightly within the aperture, and a second tapered radiation delivery portion of non-circular cross-sectional shape, projecting into the receiver chamber.
Due to the specific design of the above radiation delivery waveguide, total and Fresnel reflections of the transmitted radiation at the waveguide/second transparent medium boundary inside the receiver chamber are minimized and extraction of the delivered radiation is maximized.
The radiation delivery waveguide described above is particularly advantageous for use in the field of solar energy transfer, specifically for transferring concentrated radiation from optical concentration systems to a solar receiver. In this case, the radiation delivery waveguide as well as the concentrator constituting the first transparent medium, is made of a solid transparent medium, particularly of fused silica. However, calculations show that with large scale solar energy systems and, consequently, large scale receivers, the radiation delivery waveguide will have such dimensions that if made of solid transparent material it will be extremely heavy and expensive.
It is accordingly the object of the present invention to provide an improved, less expensive radiation delivery waveguide, and a radiation delivery assembly using such a waveguide.